Pintle for radial piston machines

ABSTRACT

A pintle for radial piston machines has two elongated control chambers separated from each other by lands and flanked by two mirror symmetrical grooves. The distance between the grooves varies periodically and the regions where the grooves are nearest to as well as most distant from each other are spaced apart from the centers of the lands, as considered in the circumferential direction of the pintle. Each groove may have a sinusoidal outline or it may consist of several arcuate sections each forming part of a circle. Alternatively, each groove may consist of straight sections which make an obtuse angle with each other.

United States Patent [191 Robeller et a1.

[ Sept. 23, 1975 PINTLE FOR RADIAL PISTON MACHINES [73] Assignee: RobertBosch G.m.b.H., Stuttgart,

Germany 22 Filed: Sept. 28, 1973 211 App]. No.: 401,942

[30] Foreign Application Priority Data [58] Field of Search 251/281,283; 91/486, 491, 91/498, 484; 137/625.24

[56] References Cited UNITED STATES PATENTS 3,280,757 10/1966 Eickmann91/498 3,430,919 3/1969 Frazier 251/283 3,810,418 5/1974 Bosch 91/498FOREIGN PATENTS OR APPLICATIONS 1,260,890 6/1960 France 91/498 649,8562/1951 United Kingdom... 91/491 827,154 1/1952 Germany 91/491 PrimaryExaminer-Martin P. Schwadron Assistant ExaminerRobert J. MillerAttorney, Agent, or Firm-Michael S. Striker [57] ABSTRACT A pintle forradial piston machines has two elongated control chambers separated fromeach other by lands and flanked by two rriirror symmetrical grooves. Thedistance between the grooves varies periodically and the regions wherethe grooves are nearest to as well as most distant from each other arespaced apart from the centers of the lands, as considered in thecircumferential direction of the pintle. Each groove may have asinusoidal outline or it may consist of several arcuate sections eachforming part of a circle. Alternatively, each groove may consist ofstraight sections which make an obtuse angle with each other.

8 Claims, 3 Drawing Figures MS Pamm Sept. 23,1975 Sheet 1 of 2 3,906,998

US Patent Sept. 23,1975 Sheet 2 M2 3,906,998

PINTLE FOR RADIAL PISTON MACES BACKGROUND OF THE INVENTION The presentinvention relates to radial piston machines in general, and moreparticularly to improvements in pintles or valves for radial pistonmachines of the type wherein a cylinder block rotates about a pintle andis provided with radially extending cylinders for reciprocable pistons,and wherein the peripheral surface of the pintle is provided with atleast two control chambers located diametrically opposite each other andcommunicating alternately with successive cylinders when the cylinderblock rotates.

It is already known to provide a pintle with two control chambers one ofwhich constitutes a high-pressure chamber and the other of whichconstitutes a lowpressure chamber. The control chambers are separatedfrom each other by platforms or lands one of which is adjacent topistons which assume their inner end positions (i.e., nearest to theperipheral surface of the pintle) and the other of which is adjacent topistons which assume their outer end positions. It is further known toprovide the peripheral surface of the pintle with recesses or grooveswhich flank the control chambers therewith elongated sealing projectionsor ribs. When the cylinder block rotates, fluid leaks from thehighpressure control chamber and establishes fields between therespective sealing projections and the internal surface of the cylinderblock whereby such pressure fields oppose a movement of the adjacentportion of the cylinder block toward the peripheral surface of thepintle. The point of attack of the resultant of forces produced by allpressure fields should coincide with or should be closely adjacent tothe point of attack of the force which acts upon the pintle. Such forceis produced in part by fluid pressure acting on ring-shaped surfaces inthose cylinders of the cylinder block which travel along thehigh-pressure control chamber of the pintle. The point of attack of thejust discussed force travels back and forth about the center of thehighpressure control chamber in and counter to the direction of rotationof the cylinder block. The length of the arc along which the point ofattack travels back and forth depends on the number of cylinders in thecylinder block.

The pistons exert lateral forces on the walls surrounding the respectivecylinders, and the resultant of such forces tends to urge the cylinderblock toward the pintle in the region of that land which is adjacent topistons assuming their inner end positions. The sum of forces generatedby fluid pressure and by the pistons produces a resultant force whichacts on the pintle in the region between the just mentioned land and thecenter of the high-pressure control chamber. The point of attack of theresultant force travels back and forth between the land and the centerof the high-pressure control chamber. In presently known radial pistonmachines, the resultant force is not always balanced by an opposingforce so that the width of the gap between the pintle and the cylinderblock fluctuates with attendant excessive leakage of pressurized fluid.

SUMMARY OF THE INVENTION An object of the invention is to provide anovel and improved pintle which can be used in radial piston pumps ormotors and which is constructed and mounted in such a way that itcontributes to automatic centering of the cylinder block by enabling thepressure fields between its peripheral surface and the internal surfaceof the cylinder block to neutralize the aforediscussed forces producedby the piston and pressurized fluid and tending to move the cylinderblock nearer to the pintle.

Another object of the invention is to provide the pintle with novel andimproved sealing projections which enable the fluid to establishpressure fields capable of opposing excessive radial movements of thecylinder block with respect to the pintle.

A further object of the invention is to provide a pintle which can beused in many existing types of radial piston machines as a superiorsubstitute for conventional pintles.

The invention is embodied in a pintle or valve which can be used in aradial piston pump or motor and has a peripheral surface provided with aplurality of control chambers having a common symmetry plane which isnormal to the axis of the pintle. The peripheral surface of the pintleis further provided with a plurality of lands alternating with thecontrol chambers, as considered in the circumferential direction of thepintle, and with two recesses or grooves flanking the control chambersand being mirror symmetrical to each other with reference to theaforementioned plane. The distance between the two recesses variesperiodically, as considered in the circumferential direction of thepintle, and the peripheral surface of the pintle includes a sectionwhich is disposed between the two recesses and has portions of maximumand minimum width which are spaced apart or offset from the lands, asconsidered in the circumferential direction of the pintle.

Each of the two recesses can have a sinusoidal outline. Alternatively,each recess may consist of several arcuate sections or portions each ofwhich forms part of a circle and which merge gradually into each other.Still further, each recess may consist of several straight sections orportions whereby the neighboring sections make an obtuse angle with eachother.

The novel features which are considered as characteristic of theinvention are set forth on particular in the appended claims. Theimproved pintle itself, however, both as to its construction and. itsmode of operation, together with additional features and advantagesthereof, will be best understood upon perusal of the following detaileddescription of certain specific embodiments with reference to theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of radialpiston machine including a pintle which embodies one form of theinvention;

FIG. 2 is a fragmentary developed view of the pintle shown in FIG. 1;and

FIG. 3 is a fragmentary developed view of a modified pintle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS stalled in the housing 1. Thecylinder block 5 has a shaft 7 which is driven by a suitable prime moverwhen the machine is operated as a pump and which receives torque fromthe cylinder block when the machine is operated as a motor.

The cylinder block 5 is formed with radially extending cylinders 8 forpistons 9 each of which is mounted in the respective cylinder with aminimum of play. The pistons 9 are provided with articulately mountedarcuate heads or shoes 10 which engage the cylindrical internal surfaceof a slide block 11 serving to determine the length of piston strokes.As shown, the slide block 11 is rigid with a spindle nut 14 meshing witha feed screw 15 which is rotatable in a bracket 16 of the housing 1. Themeans for rotating the feed screw 15 comprises a hand wheel 17. Ahelical spring 18 reacts against the housing 1 and bears against theslide block 11 diametrically opposite the nut 14.

The hand wheel 17 can be rotated to move the axis of the slide block 11above or below as well as into a position of coincidence with the axisof the pintle 4. Thus, the operator can change the stroke of each piston9 at will and can select any one of an infinite number of strokes. Thecylinders 8 include conical inner end portions 12 whose diametersdecrease in a direction toward the peripheral surface of the pintle 4and which communicate with radial ports 13 of the cylinder block 5.These ports sweep seriatim past two elongated control chambers 19, 20which are machined into the peripheral surface of the pintle 4diametrically opposite each other. As best shown in FIG. 2, the controlchambers 19, 20 are separated from each other by platforms or lands 23,24 and respectively communicate with axially parallel bores 21, 22(FIG 1) of the pintle 4.

Referring to FIG. 2, it is assumed that the cylinder block 5 rotates ina direction indicated by arrow A. The chamber 19 constitutes ahigh-pressure control chamber when the axis of the slide block 14 islocated above the axis of the pintle 3, as viewed in FIG. 1, and thechamber 20 constitutes a high-pressure control chamber if the axis ofthe slide block 14 is located at a level below the axis of the pintle.If the chamber 19 constitutes a high-pressure control chamber, the land24 is adjacent to those pistons 9 which assume their inner end positionsat a minimum distance from the peripheral surface of the pintle 4. Thosepistons which assume their inner end positions are adjacent to the land23 if the eccentricity of the slide block 14 is changed in such a waythat a control chamber 20 constitutes a highpressure chamber.

The peripheral surface of the pintle 4 is futher provided with twoendless recesses or grooves 25, 26 which are mirror symmetrical to eachother with reference to a plane 27. This plane constitutes the centralsymmetry plane of the control chambers 19, 20 and lands 23, 24, and isnornal to the axis of the pintle 4. Each of the recesses 25, 26 has asinusoidal outline. The width (as considered in the axial direction ofthe pintle 4) of that portion or section 4A of the peripheral surface ofthe pintle which extends between the recesses 25, 26 (this sectionincludes portions of the lands 23, 24 and is provided with the controlchamber 19, 20) varies periodically between several maximum and severalminimum values, as considered in the circum ferential direction of thepintle. The portions of minimum width are located between the portions28, 28' and 30, of the recesses 25, 26. The portions of maximum widthare located between the portions 29, 29'

and 31, 31 of the recesses 25, 26. It will be noted that the portions ofmaximum and minimum width of the section 4A are spaced apart from thecenters of the lands 23, 24 and from the centers of the control chambers19, 20, as considered in the circumferential direction of the pintle 4.The width of the section 4A between 28, 28' equals the width between 30,30', and the width between 29, 29 equals the width between 31, 31 Theperiodicity of the recesses 25, 26 is degrees and, as mentioned above,the nodes of the recesses are shifted in phase with respect to thecenters of the lands 23, 24.

The recesses 25, 26 define with the cortrol chamber 19 a pair ofelongated sealing projections or ribs 32, 33 whose width (as consideredin the axial direction of the pintle 4) varies continuously asconsidered in the circumferential direction of the pintle. Similarsealing projections or ribs 34, 35 are provided between the recesses 25,26 and the control chamber 20. The sealing projections 32, 33, 34, 35have portions of maximum width in the region of portions 29, 29', 31,31' of the respective recesses 25, 26, i.e., in the region of thoseportions of the recesses which are located at a maximum distance fromthe symmetry plane 27. The width of the control chambers 19, 20 isconstant. The imaginary centers of the sealing projections 32, 33 arelocated between the center of the control chamber 19 and the land 24(i.e., that land which is located downstream of the control chamber 19,as considered in the direction indicated by arrow A). Analogously, thecenters of sealing projections 34, 35 are shifted from the center of thecontrol chamber 20 toward the land 23.

The recesses 25, 26 are flanked by two carrying and sealing elements orrings 36, 37 which constitute portions of the peripheral surface of thepintle 4. The sealing element 36 extends all the way to the inner axialend of the pintle.

It is assumed that the chamber 19 constitutes a highpressure chamber andthat the cylinder block 5 rotates in the direction indicated by arrow Awhile the radial piston machine operates as a pump, i.e., the shaft 7 isassumed to be driven by an electric motor or the like. Some pressurizedfluid leaks from the control chamber 19, through the gap between thesealing projections 32, 33 and the internal surface of the cylinderblock 5, and into the adjacent portions of recesses 25, 26. Such fluidestablishes pronounced pressure fields between the sealing projections32, 33 and the cylinder block. Pressurized fluid also leaks from therecesses 25, 25, between the sealing elements 36, 37 and the internalsurface of the cylinder block 5, and into the interior of the housing 1.Moreover, and if the fluid pressure in the control chamber 20 is lessthan in the recesses 25, 26, the fluid also flows from the recesses,between the sealing projections 34, 35 and the internal surface of thecylinder block 5, and into the control chamber 20. This results in areduction of fluid pressure in the recesses 25, 26 so that such pressureequals the pressure in the control chamber 20. The pressure fields whichdevelop between the sealing elements and projections 36, 37, 34, 35 onthe one hand and the internal surface of the cylinder block 5 on theother hand are less pronounced that the pressure fields in the region ofsealing projections 32, 33. The less pronounced pressure fieldscompensate each other, either completely or substantially, i.e., thepoint of attack of a force produced by all pressure fields is close toor coincides with the point of at-- tack of the force produced bypressure fields-in the region of sealing projections 32, 33. Thus, theforce which is produced by pressure fields in the region of projections32, 33: contributestalmost exclusively to equalization of forces whichact upon the pintle-4.

The sinusoidal outlineof the recesses 25, 26'insures that the, centersofpressure-fields in the region of the sealing projections 32, 33, 34,35- areshifted in a-direc phase and the amplitudes ojfthe recesses 25,26areselected in such a way thatthe point pf'attack of the resultant of.all forces acting on the pintle 4 coincides with the point of attack ofthe resultant of forces produced by all pressure fields whereby the'twoforces neutralize each other. The amplitude of the recesses 25, 26determines the maximum and minimum width of the section 4A of theperipheral surface of the pintle 4, and the shift in phase of therecesses 25, 26 determines the distance between the portions 2831 and28'-3l' of the recesses 25, 26 with respect to the centers of thecontrol chambers 19, and the centers of lands 23, 24.

An advantage of the improved pintle is that the sealing projectionsestablish the relatively large pressure fields which produce substantialforces in regions where the pintle is stressed by forces generated byfluid pressure and pistons in the cylinders of block 5. The forcesgenerated by pressure fields render it possible to enhance theneutralization of forces acting on the pintle so that the cylinder blockis centered during each stage of operation of the radial piston machine.

The pintle 4 of FIG. 2 can be modified by replacing the sinusoidalrecess 25, 26 with recesses each of which consists of several arcuatesections which merge gradually into each other and each of whichconstitutes a portion of a circle. For example, the recess can bereplaced by a recess having two arcuate portions (in the region of 28,whose convex sides face the sym metry plane 27, and two arcuate portions(in the region of 29, 31) whose convex sides face the plane 27. Theother recess is mirror symmetrical to the just discussed recess theradii of curvature of arcuate portions of such recesses can be readilyselected in such a way that the resultant of all forces produced by thepressure fields between the pintle and the cylinder block equals andbalances the resultant of all forces acting upon the pintle per unit oftime.

FIG. 3 illustrates a portion of a modified pintle 40 wherein all suchparts which are identical with or clearly analogous to the correspondingparts shown in FIG. 2 are denoted by similar reference characters. The

recesses or grooves 41, 42 respectively replace the reof each recessmakean beta and each section makes withthe, symmetryplane 27 an acuteangle alpha. Each of the recesses 41, 42 is a circumferentially completegroove and these recessesrespectively define with the control charnbers19,20 pairs of sealing projections or ribs. '47,,48 and149, 50. Thecenters of the sealing projections 47-50 arejshifted in a direction fromthe respective control chambers 19, 20 toward the lands 24,- 23, i.e.,in the direction of rotation of the cylinderblo'ck (arrow A). The widthof the section 40A of the. peripheral surface of the pintle 40 variesperiodically between two maximum and two minimum values substantially inthe same way as described in connection with the section 4A. Theportions of maximum width are locatedbetween 44, 44' and 46, 46', andthe portions of minimum width are located'betwe'en 43, 43

and 45, l

The reference characters 51 and 52 denote two sealing or carryingelements whichare respectively adjacent'to the recesses 41', 42 andcorrespond to the sealing elements 36, 37 of'FIG. 2,.

The portions of maximum and minimum width of the section 40A of theperipheral surface of the pintle 40 are again shifted with respect tothe centers of the control chambers 19, 20 and lands 23, 24, asconsidered in the circumferential direction of the pintle. Theperiodicity of the recesses 41, 42 equals 11 and each of these recessesis shifted in phase with respect to the centers of land 23, 24 in amanner as described above for the recesses 25, 26, i.e., so that theresultant of forces produced by all of the pressure fields balances andopposes the resultant of all forces acting on the pintle 40. This is dueto the fact that the centers of sealing projections 47, 48 are locatedbetween the center of the control chamber 19 and the center of the land24, and the centers of sealing projections 49, are located between thecenter of the control chamber 20 and the center of the land 23. Thedesigner can readily select the amplitude and the phase shift of therecesses 41, 42 in such a way that the resultant of forces produced byall pressure fields between the pintle 40 and the internal surface ofthe cylinder block is equal to and opposes the resultant of all forceswhich act on the pintle 40 per unit of time. This insures a highlysatisfactory centering of the cylinder block and reduces the leakage ofpressurized fluid from the high-pressure control chamber toward theinterior of the housing of the radial piston machine. Without furtheranalysis, the foregoing will so fully reveal the gist of the presentinvention that others can, by applying current knowledge, readily adaptit for various applications without omitting features which fairlyconstitute essential characteristics of the generic and specific aspectsof out contribution to the art and,

therefore, such adaptations should and are intended to be comprehendedwithin the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. For use in a radial piston machine, a pintle having a cylindricalperipheral surface provided with a plurality of control chambers havinga common symmetry plane normal to the axis of the pintle, saidperipheral surface including a plurality of lands alternating with saidcontrol chambers, as considered in the circumferential direction of thepintle, and said surface further having two recesses each constituted bya circumferentially complete groove of unobstructed cross section,

flanking said control chambers and being mirror symmetrical to eachother with reference to said plane, the distance between said recessesvarying periodically, as considered in the circumferential direction ofthe pintle, and said peripheral surface including a section locatedbetween said recesses and having portions of maximum and minimum widthwhich are spaced apart from the centers of said lands, as considered inthe circumferential direction of the pintle.

2. A pintle as defined in claim 1, wherein each of said recesses has asinusoidal outline.

3. A pintle as defined in claim 1, wherein each of said recessescomprises a plurality of successive straight portions and the successiveportions of each of said recesses make an obtuse angle with each other.

4. A pintle as defined in claim 1, wherein each of said lands isdisposed intermediate a portion of maximum width and a portion ofminimum width of said section, as considered in the circumferentialdirection of the pintle.

5. A pintle as defined in claim 1, wherein said control chambers areelongated, as considered in the circumferential direction of the pintle,each of said control chambers having a central portion disposedintermediate a portion of maximum width and a portion of minimum widthof said section, as considered in the circumferential direction of thepintle.

6. A pintle as defined in claim 1, wherein the periodicity of each ofsaid recesses is 7. A pintle as defined in claim 6, wherein said sectionof said peripheral surface includes two portions of maximum width andtwo portions of minimum width, said lands including a pair of landsdisposed diametrically opposite each other, one of said portions ofmaximum width being nearer to one of said pair of lands and the otherportion of maximum width being nearer to the other of said pair oflands.

8. A pintle as defined in claim 1, wherein said control chambers areelongated, as considered in the circumferential direction of the pintle,and have a constant width, as considered in the axial direction of thepintle.

1. For use in a radial piston machine, a pintle having a cylindricalperipheral surface provided with a plurality of control chambers havinga common symmetry plane normal to the axis of the pintle, saidperipheral surface including a plurality of lands alternating with saidcontrol chambers, as considered in the circumferential direction of thepintle, and said surface further having two recesses each constituted bya circumferentially complete groove of unobstructed cross section,flanking said control chambers and being mirror symmetrical to eachother with reference to said plane, the distance between said recessesvarying periodically, as considered in the circumferential direction ofthe pintle, and said peripheral surface including a section locatedbetween said recesses and having portions of maximum and minimum widthwhich are spaced apart from the centers of said lands, as considered inthe circumferential direction of the pintle.
 2. A pintle as defined inclaim 1, wherein each of said recesses has a sinusoidal outline.
 3. Apintle as defined in claim 1, wherein each of said recesses comprises aplurality of successive straight portions and the successive portions ofeach of said recesses make an obtuse angle with each other.
 4. A pintleas defined in claim 1, wherein each of said lands is disposedintermediate a portion of maximum width and a portion of minimum widthof said section, as considered in the circumferential direction of thepintle.
 5. A pintle as defined in claim 1, wherein said control chambersare elongated, as considered in the circumferential direction of thepintle, each of said control chambers having a central portion disposedintermediate a portion of maximum width and a portion of minimum widthof said section, as considered in the circumferential direction of thepintle.
 6. A pintle as defined in claim 1, wherein the periodicity ofeach of said recesses is 180*.
 7. A pintle as defined in claim 6,wherein said section of said peripheral surface includes two portions ofmaximum width and two portions of minimum width, said Lands including apair of lands disposed diametrically opposite each other, one of saidportions of maximum width being nearer to one of said pair of lands andthe other portion of maximum width being nearer to the other of saidpair of lands.
 8. A pintle as defined in claim 1, wherein said controlchambers are elongated, as considered in the circumferential directionof the pintle, and have a constant width, as considered in the axialdirection of the pintle.